Silencer and electronic equipment

ABSTRACT

A silencer is disclosed that includes a housing having a flat enclosing shape and having formed therein a passage for silencing; and pores, being formed at the housing so as to be communicatively connected with the passage, into which a sound wave to be noise is introduced. The pores, being formed close to the periphery of the housing, are configured so that the sound wave travels in the planar direction of the housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. continuation application filed under 35 USC 111(a) claiming benefit under 35 USC 120 and 365(c) of PCT application JP02/13679, filed Dec. 26, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a technology for silencing fan noise, and particularly relates to a silencer suitable for use in a fan-noise silencing process and electronic equipment having provided therein the silencer.

2. Description of the Related Art

In recent years and continuing, as small-sized electronic equipment such as a notebook PC and a desk-top PC is made smaller and faster, the amount of heat dissipation required for a semiconductor apparatus (such as a CPU) set up inside is on the increase. It is possible to air-cool using a fan as means for cooling the semiconductor apparatus.

However, with the method of cooling using the fan, there is a problem such that increasing the number of rotations of the fan in order to increase the cooling efficiency results in increased fan noise. Moreover, while only a small-sized fan can be fit into the downsized electronic equipment as described above, it is known that with the same air amount, the smaller the fan the larger the fan noise.

On the other hand, in order to reduce the fan noise without degrading the cooling performance, methods are possible such as cooling using cooling water as in water-cooling, and by means of temperature control, decreasing the number of rotations of the fan when the temperature of the CPU is low.

However, with the water-cooling, the structure of the apparatus becomes complicated so as to cause an increased product cost, and the enlarged apparatus runs counter to the demand for downsizing. Moreover, a problem arises such that an increased number of components leads to an increased failure rate, so as to cause decreased reliability of the electronic equipment into which the water-cooled cooling apparatus is fit.

With temperature control being configured to sense with a sensor an increase in the amount of heat dissipation of the CPU and to subsequently activate the fan for ventilation, the fan noise fluctuates depending on the change in the CPU operating state and room temperature. Such fluctuating is recognized by a human being as annoying noise. Moreover, when the CPU continues to operate for more than or equal to a certain time period, there is a case such that the number of rotations of the fan becomes the maximum so that there is no longer any advantage in controlling the number of rotations.

Thus, in the method of reducing the noise generated at the fan, the noise cannot be suppressed effectively. Therefore, a method is possible that uses a silencer for silencing the noise generated at the fan rather than decreasing the noise generated at the fan. However, conventionally, such method of using a silencer is used in a relatively large apparatus such as an air-conditioning apparatus but not in smaller-sized electronic equipment such as a PC. This is due to the following reasons:

-   -   1) It is considered that a large space for the silencer is         needed in order to silence the low-frequency fan noise of         approximately 500 Hz to 2 kHz;     -   2) The frequency characteristics of the fan noise are such that         the fan noise consists of multiple peak frequencies and a         wide-bandwidth component so that an adequate silencing effect         cannot be obtained with a conventional silencer with which a         single frequency can be silenced.

FIG. 1 illustrates the state in which a silencer 10 being configured conventionally is set up at a duct 2 of a fan 1. Cooling air generated at the fan 1 travels within the duct 2 in the direction of the arrow illustrated and cools a CPU, etc., as material to be cooled. This fan 1 operates at all times, or stops/rotates depending on the temperature of the materials to be cooled as in the temperature control described above.

The silencer 10 is configured such that multiple pores 12 are formed at a housing 11. As this silencer 10 is to be fit into small-sized electronic equipment such as a notebook PC and a desktop PC, the housing 11 has a flat enclosing shape. Moreover, a top plate 13 of the housing 11 is being exposed to the duct 2, and the multiple pores 12 (24 in the illustrated example) are formed at this top plate 13.

As the housing 11 has the enclosing shape as described above, an air layer for silencing is being formed. Thus, the noise that is generated by the fan 1 and that penetrates into the housing 11 from the pores 12 is silenced by attenuation through resonance and expansion at the air layer within this housing 11.

Now each parameter of the silencer 10 is set as follows while illustrating each of these parameters in FIG. 1:

-   -   c: the speed of sound (m/s)     -   t: the plate thickness of the top plate 13 (mm);     -   φ: the diameter of the pores 12 (mm);     -   L: the length of the noise passage (mm);     -   D: the interval between the pores 12 (mm);     -   P: the intermediate value;     -   f: the silencing frequency (Hz)

When specifying each parameter as described above, the silencing frequency f (Hz) silenceable at the silencer 10 and the intermediate value P may be represented by the following equations (1) and (2): f=c/2π{square root}{square root over (P/(t+)}0.8φ)L  (1) P=πφ ²/4D ²  (2)

Now, there is more demand for downsizing the silencer to be fit into small-sized electronic equipment relative to the conventional silencer fit in large-sized equipment such as an air-conditioning apparatus so that the constraint on the size of the silencer to be fit into the small-sized electronic equipment is severe. More specifically, the thickness of the housing 11 may be constrained to be within 0.5 mm. Then, the length L of the noise passage in equation (1) as described above is equivalent to the distance from the pores 12 to the bottom of the housing 11, or in other words, the thickness of the housing 11.

Now, assuming the speed of sound c as 346.3 m/s, the plate thickness t of the top plate 13 as 0.5 mm, the diameter φ of the pores 12 as 0.8 mm, the length L of the noise passage (or the thickness of the housing 11) as 0.5 mm, and the interval D between the pores 12 as 10 mm; according to the equations (1) and (2), the silencing frequency f ends up high at f=5176 Hz such that the fan noise (at approximately 1.5 to 2 kHz) actually generated at the fan 1 cannot be silenced.

Thus, in the conventional silencer 10, when it is fit into small-sized electronic equipment such as a notebook PC and a desktop PC, the length L of the noise passage cannot be increased so that the fan noise generated at the fan 1 cannot be silenced. Moreover, when the configuration is made such that the fan noise generated at the fan 1 is reliably eliminated, there is a problem in that the silencer 10 ends up being large such that a further demand for downsizing the small-sized electronic equipment cannot be met.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a technology for silencing fan noise that substantially obviates one or more problems caused by the limitations and disadvantages of the related art.

It is a more particular object of the present invention to provide a silencer for use in a fan-noise silencing process and electronic equipment having provided the silencer that achieves silencing reliably while achieving downsizing.

According to the invention, a silencer includes a housing having a flat enclosing shape and having formed therein a passage for silencing, and one or a plurality of pores, being formed at the housing so as to be communicatively connected with the passage, into which a sound wave to be noise is introduced, wherein the pores, being formed close to the periphery of the housing, are configured so that the sound wave to be noise travels in the planar direction of the housing.

The silencer as described above enables achieving silencing reliably while achieving downsizing.

According to another aspect of the invention, in electronic equipment including within the apparatus mainframe a fan for cooling and a silencer for silencing noise generated at the fan, the silencer includes a housing having a flat enclosing shape and having formed therein a passage for silencing, and one or more pores, being formed at the housing so as to be communicatively connected with the passage, into which a sound wave to be noise is introduced, and the pores, being formed close to the periphery of the housing, are configured so that the sound wave to be noise travels in the planar direction of the housing.

The electronic equipment as described above enables achieving silencing reliably while achieving downsizing.

Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing a configuration of an exemplary conventional silencer and a theoretical equation regarding the silencing frequency;

FIG. 2 is a block diagram of a silencing apparatus being a first embodiment of the present invention;

FIG. 3 is a cross-sectional view of the silencing apparatus being the first embodiment of the present invention;

FIG. 4A is a diagram illustrating the silencing performance of the silencer being the first embodiment of the present invention relative to the silencing performance of a conventional silencer;

FIG. 4B is a diagram illustrating the silencing effect of the silencer being the first embodiment of the present invention;

FIG. 5A is a diagram illustrating the silencing performance of a silencer not being enclosed;

FIG. 5B is a diagram illustrating the silencing effect of the silencer not being enclosed;

FIG. 6 is a block diagram of a silencing apparatus being a second embodiment of the present invention;

FIG. 7 is a cross-sectional view of the silencing apparatus being the second embodiment of the present invention;

FIG. 8 is a cross-sectional view of a silencing apparatus being a third embodiment of the present invention;

FIG. 9 is a block diagram of a silencing apparatus being a fourth embodiment of the present invention;

FIG. 10 is a cross-sectional view of the silencing apparatus being the fourth embodiment of the present invention;

FIG. 11 is a block diagram of a silencing apparatus being a fifth embodiment of the present invention;

FIG. 12 is a cross-sectional view of the silencing apparatus being the fifth embodiment of the present invention;

FIG. 13 is a block diagram of a silencing apparatus being a sixth embodiment of the present invention;

FIG. 14 is a cross-sectional view of a silencing apparatus being the sixth embodiment of the present invention;

FIG. 15 is a cross-sectional view of a silencing apparatus being a seventh embodiment of the present invention;

FIG. 16 is a cross-sectional view of a silencing apparatus being an eighth embodiment of the present invention;

FIG. 17 is a cross-sectional view of a silencing apparatus being a variant of the eighth embodiment of the present invention;

FIG. 18 is a cross-sectional view of a silencing apparatus being a ninth embodiment of the present invention;

FIG. 19 is a cross-sectional view illustrating the state before operating a silencing apparatus being a tenth embodiment of the present invention;

FIG. 20 is a cross-sectional view illustrating the state after operating the silencing apparatus being the tenth embodiment of the present invention;

FIG. 21 is a cross-sectional view illustrating the state before operating a silencing apparatus being an eleventh embodiment of the present invention;

FIG. 22 is a cross-sectional view illustrating the state after operating the silencing apparatus being the eleventh embodiment of the present invention;

FIG. 23 is a cross-sectional view of a silencing apparatus being a twelfth embodiment of the present invention;

FIG. 24 is a plan view illustrating the state before operating the silencing apparatus being the twelfth embodiment of the present invention;

FIG. 25 is another plan view illustrating the state after operating the silencing apparatus being the twelfth embodiment of the present invention;

FIG. 26 is a cross-sectional view from the right-hand side of the silencing apparatus being the twelfth embodiment of the present invention;

FIG. 27 is a perspective view of the silencing apparatus being a thirteenth embodiment of the present invention;

FIG. 28 is a cross-sectional view illustrating the state before operating the silencing apparatus being the thirteenth embodiment of the present invention;

FIG. 29 is a cross-sectional view illustrating the state after operating the silencing apparatus being the thirteenth embodiment of the present invention;

FIG. 30 is a perspective view of a silencing apparatus being a fourteenth embodiment of the present invention;

FIG. 31 is a (first) diagram for describing a mounting structure of the silencing apparatus being the fourteenth embodiment of the present invention;

FIG. 32 is a (second) diagram for describing the mounting structure of the silencing apparatus being the fourteenth embodiment of the present invention;

FIG. 33 is a cross-sectional view of the silencing apparatus being the fourteenth embodiment of the present invention;

FIG. 34 is a cross-sectional view of the silencing apparatus being a first variant of the fourteenth embodiment of the present invention;

FIG. 35 is a cross-sectional view of the silencing apparatus being a second variant of the fourteenth embodiment of the present invention;

FIG. 36 is a cross-sectional view of the silencing apparatus being a third variant of the fourteenth embodiment of the present invention;

FIG. 37 is a perspective view of the silencing apparatus being a fifteenth embodiment of the present invention; and

FIG. 38 is a perspective view of electronic equipment into which each of the silencing apparatuses corresponding to each of the embodiments of the present invention is fit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are described with reference to the accompanying drawings.

FIGS. 2 and 3 illustrate a silencer 20A being a first embodiment of the present invention. It is noted that the same elements in FIGS. 2, 3, and each of the subsequent figures used in describing each embodiment as the elements illustrated in FIG. 1 have applied the same letters.

The silencer 20A in the present embodiment is configured from a housing 21 and pores 22 being formed at a top plate 23 of this housing 21. The housing 21 has a flat enclosing shape and is configured to be enclosed except for the pores 22. Therefore, a space (below referred to this space as an air layer 24) is formed within the housing 21. This housing 21 is set up at a duct 2 of a fan 1 generating cooling air.

The fan 1 and the duct 2 are set up within an apparatus mainframe 72 of electronic equipment 70 such as a desktop PC as illustrated in FIG. 38 so that materials to be cooled such as a CPU, etc., are cooled by cooling air generated at the fan 1. It is noted that applying the present invention is not to be limited to a desktop PC such that the present invention may be applied to a further-downsized notebook PC or a large-sized server.

The housing 21 is mounted onto the duct 2 such that the top plate 23 is exposed within the duct 2. Thus, the sound wave to be noise generated at the fan 1 penetrates from the pores 22 into the housing 21. It is noted that the arrow represented by the letter N illustrates the penetrating of the sound wave to be noise into the housing 21.

The pores 22 for introducing the sound wave to be noise into the housing 21 are formed close to the periphery of the housing 21. More specifically, a multiple number (4 in the present embodiment) of pores are formed along the short side of one end which is upstream relative to the direction (represented as arrow “a” in FIG. 2) of flow of the cooling air generated at the fan 1. It is noted that while the pores 22 are formed along the short side on the one upstream end relative to the direction of the flow of the cooling air in the present embodiment, the configuration may be such that the pores 22 are formed along the short side of the other downstream end relative to the direction “a” of the flow of the cooling air.

Thus, having formed the pores 22 close to the periphery of the housing 21 causes the sound wave to be noise that has penetrated from the pores 22 to travel in the planar direction (the direction parallel to the direction “a” of the flow of the cooling air) in the air layer 24 that is formed within the housing 21 and that is to be the passage for the sound wave. Then, the distance that the sound wave to be noise travels within the housing 21 becomes the distance represented by the arrow “L” in FIGS. 2 and 3 so as to be a larger distance relative to the thickness dimension W of the housing 21 (L>W).

Now focusing on equation (1) as described above, out of the various parameters, the length L of the noise passage in the present embodiment becomes the distance L that the sound wave to be noise travels within the housing 21. The length L of this noise passage is a value in the denominator so that as the value L gets larger the silencing frequency f becomes smaller. Therefore, according to the silencer 20A of the present embodiment, even making the thickness W of the housing 21 smaller to achieve downsizing, or in other words even achieving downsizing of the silencer 20A enables decreasing the silencing frequency f, enabling effectively silencing the noise generated at the fan 1 that is of low frequency.

Next, a calculation is made by substituting specific parameter values into equation (1). Now, each of the parameter values in equation (1) is set equal to the parameter values used when deriving the silencing frequency f of the silencer 10 previously illustrated in FIG. 1. More specifically, the parameters are set with the speed of sound c as 346.3 m/s, the plate thickness t of the top plate 13 as 0.5 mm, the diameter φ of the pores 12 as 0.8 mm, the interval D between the pores 12 as 10 mm, and the length L of the noise passage as 4 mm in the present embodiment (L=0.5 mm in the example illustrated in FIG. 1).

As a result, the silencer 20A in the present embodiment, without changing to a large extent the shape relative to the silencer 10 as illustrated in FIG. 1, or in other words while achieving downsizing of the silencer 20A, a large reduction from the previous f=5176 Hz to f=1830 Hz is enabled. This silencing frequency f=1830 Hz (below referred to as the theoretical frequency value) becomes the roughly-center frequency of the fan noise (approximately 1.5 to 2 kHz) actually generated at the fan 1. Therefore, with the silencer 20A of the present embodiment, effectively silencing the fan noise generated at the fan 1 is enabled.

FIG. 4A illustrates the silencing performance of the silencer 20A in the present embodiment in relation to the silencing performance of the conventional silencer as illustrated in FIG. 1. Moreover, FIG. 4B is a diagram illustrating the silencing effect of the silencer being the first embodiment of the present invention, and more specifically represents the result of having subtracted the value after applying the silencer from the value before applying the silencer as illustrated in FIG. 4A.

According to these figures, the silencing frequency f of the silencer 20A in the present embodiment is 1810 Hz to 1840 Hz so as to roughly correspond to 1830 Hz being the theoretical frequency value derived from equation (1). More specifically, as illustrated in FIG. 4B, it can be understood that, as a large noise-reducing effect of approximately 20 dB (A) centered at 1840 Hz is obtained, an effective silencing is performed on the noise of the fan 1.

On the other hand, FIG. 5A illustrates the silencing performance of the silencer 20A when there is a gap at a portion of the housing 21 so that the air layer 24 is communicatively connected to outer air. The silencing performance of the conventional silencer as illustrated in FIG. 1 is also illustrated in this figure as well. Furthermore, FIG. 5B illustrates the silencing effect of the silencer 20A having formed the gap.

According to FIG. 5A, 5B, with the silencer 20A that has the gap in the housing 21 so that the airproofness of the housing 21 is reduced, the peak of the silencing frequency f is 2848 Hz so as not to coincide with the theoretical frequency value of f=1830 Hz.

Thus, it can be understood that effectively silencing the noise of the fan 1 requires enclosing the air layer 24 formed within the housing 21. Having to enclose the housing 21 except at the positions at which the pores 22 are formed, enables suppressing the so-called noise leakage, thus enabling to reliably absorb resonance within the housing 21.

Next, a second embodiment of the present invention is described.

FIGS. 6 and 7 illustrate a silencer 20B being the second embodiment. The silencer 20B in the present embodiment is characterized in that a partition plate 25 is provided within the housing 21 in the silencer 20A in the first embodiment. It is noted that in each of the diagrams for use in describing the second and the subsequent embodiments, the same elements as the elements illustrated in FIGS. 1 and 2 have applied the same letters so as to omit the explanations for the elements.

This partition plate 25 is being set up so as to be roughly parallel to the direction “a” of flow of the cooling air generated at a fan 1 and also to be roughly parallel to a top plate 23. Also, the partition plate 25 has the edge of the side which is upstream relative to the direction of the flow of the cooling air (the left-hand side in FIG. 7) fixed to the inner wall of the housing 21.

By configuring as described above, an air layer 24 formed within the housing 21 is partitionally formed into upper and lower sections so that two passages consisting of an upper passage 26 and a lower passage 27 are formed. Then, the sound wave to be the noise introduced from pores 22 travels through the upper-section passage 26 so as to further travel into the lower-level passage 27.

Thus, in the silencer 20B in the present embodiment, even the housing 21 having the same shape as that of the silencer 20A in the first embodiment enables providing a longer distance for the sound wave to be noise to travel relative to the configuration of the silencer 20A in the first embodiment which is not provided a partition plate. More specifically, the distance for the sound wave to be noise to travel within the housing 21 may be roughly doubled from L with the silencer 20A in the first embodiment to 2×L according to the present embodiment. Hereby, further decreasing the silencing frequency f while maintaining the small size of the silencer 20B is enabled.

It is noted that while an example of having provided one partition plate 25 within the housing 21 is described, the number of the partition plates 25 provided within the housing 21 is not limited to one so that a configuration of having provided multiple partition plates is possible. Moreover, it is possible to change the length of each of the partition plates 25. Thus, appropriately setting the number of partition plates 25 to be set up and the length of the partitioning plates enables implementing a silencer having a random silencing frequency f.

Next, a third embodiment of the present invention is described.

FIG. 8 illustrates a silencer 20C being the third embodiment. The silencer 20C in the present embodiment is characterized in that sound-reflecting plates 28 are provided at the upper passage 26 and the lower passage 27 that are divided by the partition plate 25 in the silencer 20B being the second embodiment.

These sound-reflecting plates 28, being provided at the position at which the sound wave to be noise that is introduced from a pore 22 is reflected within a housing 21, perform a function of guiding at this reflecting position the direction of the reflecting to the direction to which each of the passages 26 and 27 extends. Therefore, each of the sound-reflecting plates 28 is set up so as to have approximately a 45-degree angle relative to a top plate 23 and the partition plate 25.

Thus, having provided within the housing 21 the sound-reflecting plates 28 for guiding the sound wave to be noise enables efficient guiding of the sound wave to be noise to each of the passages 26 and 27, enabling improving the silencing efficiency. Moreover, with it being necessary to provide within the housing 21 only the sound-reflecting plates which are merely plate materials, there is no need to cause the size of the silencer 20C to increase as a result.

Now a fourth embodiment of the present invention is described.

FIGS. 9 and 10 illustrate a silencer 20D being a fourth embodiment. The silencer 20D in the present embodiment is characterized by having formed multiple pores 22 in a housing 21 while having made the height positions from a surface of the housing 21, from which the pores 22 are exposed, to differ.

Out of a total of 12 pores 22 of which are formed in the silencer 20D in the present embodiment, four pores 22A being close to a fan 1 are configured such that upward-projecting pipes 29 are upwardly erected from a top plate 23 so that the pores 22A are exposed at the top end of these upward-projecting pipes 29.

Moreover, four pores 22C being farthest from the fan 1 are configured such that downward-projecting pipes 30 are downwardly erected from the top plate 23 so that the pores 22C are exposed at the bottom end of these downward-projecting pipes 30. Furthermore, the pores 22B set up between the pores 22A and the pores 22C are configured such that the pores are directly formed on the top plate 23.

Now assuming the height of the upward-projecting pipe 29 in the upward direction from the top plate 23 to be t1 and the height of the downward-projecting pipe 30 in the downward direction from the top plate 23 to be t2, each of these heights t1 and t2 become equivalent to the plate thickness t of the top plate 13 in the equation (1) as described above.

In the equation (1), as the plate thickness t of the top plate 13 is in the denominator, the larger the plate thickness t the smaller the silencing frequency f. Thus, changing the heights t1 and t2 of the projecting pipes 29, 30, respectively, enables adjusting the value of the silencing frequency f. Hereby, silencing noises of various frequencies is enabled, enabling wide-bandwidth silencing. Moreover using pipes 29, 30 for making the height positions from the surface of the housing 21, from which the pores 22 are exposed, to differ, enables easy and inexpensive adjusting of the silencing frequency f.

Furthermore, it is known that the noise generated at the fan 1 is greatest at the center position of the duct 2 and less towards the periphery. In the present embodiment, the upward-projecting pipes 29 are configured such that they extend into the duct 2 so that the pores 22 being positioned at the tip of the upward-projecting pipes 29 are exposed at the positions at which the noise within the duct 2 is great. Thus, compared with the pores 22B and the pores 22C, efficiently introducing noise within the duct 2 into the housing 21 (the air layer 24) is enabled, enabling increasing the silencing efficiency.

Next a fifth embodiment of the present invention is described.

FIGS. 11 and 12 illustrate a silencer 20E being the fifth embodiment. The silencer 20E in the present embodiment is configured such that varying the wall thickness of a housing 21 varies the depths of pores 32A through 32C formed in this housing 21.

More specifically, in the present embodiment, a top plate 31 configuring the housing 21, as illustrated in FIG. 12, is arranged such as to have a sectionally-triangular shape, and to have the thickness to gradually increase toward the end which is downstream relative to the direction “a” of the flow of cooling air. Then, as illustrated, at the top plate 31, pores are made that consist of 3 pores 32A having the depth t1, 3 pores 32B having the depth t2, and 3 pores 32C having the depth t3 (where t1<t2<t3).

The thicknesses t1 through t3 of these pores 32A through 32C, respectively, become equivalent to the plate thickness t of the top plate 13 in the equation (1) as described above. As described previously, as the plate thickness t of the top plate 13 in the equation (1) is in the denominator, the larger the plate thickness t the smaller the silencing frequency f.

Thus, changing the depths t1 through t3 of each of the pores 32A through 32C by changing the tilt angle of the top plate 31 enables adjusting the value of the silencing frequency f. Hereby, silencing the noise of various frequencies is enabled, enabling wide-bandwidth silencing.

Next a sixth embodiment of the present invention is described.

FIGS. 13 and 14 illustrate a silencer 20F being a sixth embodiment. The silencer 20F in the present embodiment is configured such that having to tilt a bottom plate 34A of a housing 21 varies the distances L1 through L3 to a bottom plate 34A from pores 33A through 33C, respectively, formed at this housing 21 (L3<L2<L1).

Furthermore, in the silencer 20F in the present embodiment, it is configured such that the diameter φ2 of the pores 33B positioned at the center relative to the direction “a” of flow of cooling air is made larger than the diameter φ1 of the pores 33A and 33C positioned on both sides of the pores 33B (φ2>φ1).

The distances L1 through L3 to the bottom plate 34A from these pores 33A through 33C, respectively, become equivalent to the length L of the noise passage in the equation (1). As described previously, the length L of the noise passage in the equation (1) is in the denominator, so the larger the noise passage L the smaller the silencing frequency f.

Thus, changing the tilt angle of the bottom plate 34A so as to change the distances L1 through L3 enables adjusting the value of the silencing frequency f. Hereby, silencing noises of various frequencies is enabled, enabling wide-bandwidth silencing.

Moreover in the present embodiment, the diameter φ2 of the pores 33B is set larger than the diameter φ1 of the pores 33A and 33C (φ2>φ1). According to equations (1), (2) as described above, the larger the diameter of the pore the larger the silencing frequency f. Thus, even changing the diameters φ1, φ2 of the pores 33A through 33C enables adjusting the value of the silencing frequency f, enabling wide-bandwidth silencing.

FIG. 15 illustrates a silencer 20G being a seventh embodiment of the present invention. The shape of a bottom plate 34 is not limited to a tilted plane as in the sixth embodiment, but may be spherically shaped as in the present embodiment.

Next an eighth embodiment of the present invention is described.

FIG. 16 illustrates a silencer 20H being an eighth embodiment of the present invention. Moreover, FIG. 17 illustrates a silencer 20I being a variant of the eighth embodiment. The silencer 20H in the eighth embodiment is characterized by having formed a concave section 35 at a portion of a top plate 23 of a housing 21, while the silencer 20I being the variant is characterized by having formed a convex section 36 at a portion of the top plate 23 of the housing 21.

As in each of the embodiments, having to form the concave section 35 or the convex section 36 at the top plate 23 enables causing the distances L2 and L3 between a pore 22 formed at either the concave section 35 or the convex section 36 and a bottom plate 34 of the housing 21, and the distance L1 between a pore 22 formed at the top plate 23 and the bottom plate 34 of the housing 21, to differ.

The distances L1 through L3 to the bottom plate 34 from the corresponding pores 22 are equivalent to the length L of the noise passage in the equation (1) as described above. Thus as in the present embodiment, even forming the concave section 35 or the convex section 36 at the top plate 23 enables adjusting the value of the silencing frequency f.

Next a ninth embodiment of the present invention is described.

FIG. 18 illustrates a silencer 20J being the ninth embodiment. While a plate material such as a metal plate is used as the top plate 23 in each of the embodiments as described above, the silencer 20J in the present embodiment is characterized in that a face of a housing 21 that is being exposed into a duct 2 is configured from a film 37. As this film 37, a polyimide film may be used, for example.

As in the present embodiment, using the film 37 in lieu of the top plate 23 made of the plate material such as the metal plate enables making the diameter φ of pores 22 being formed at the film 37 smaller than the diameter of the pores being formed at the top plate 23 in other embodiments. In other words, it is known that, when attempting to form a pore at a certain substrate, the diameter of this pore correlates with the thickness of the substrate at which the attempt is made to form the pore, so that the thicker the substrate the larger the minimum diameter of the pore. Moreover, forming a fine pore at a thick substrate requires large-scale facilities resulting in an increased machining cost.

The film 37 may be made thinner than the top plate 23 being used in the other embodiments. Thus according to the present embodiment, easy and inexpensive forming at the film 37 of the pores 22 having the diameter φ smaller than those of the pores in the other embodiments is enabled.

As described above, the silencing frequency f becomes larger the larger the diameter φ of the pores 22 according to equations (1), (2). Thus, being able to make the diameter φ of the pores 22 smaller as in the present embodiment enables making the value of the silencing frequency f smaller, enabling effective silencing of specifically the low frequency range.

Now a tenth embodiment of the present invention is described.

FIGS. 19 and 20 illustrate a silencer 20K being the tenth embodiment. In each of the embodiments as described above, the housing 21 is configured to have an enclosing shape and to not deform from the enclosing shape. On the other hand, the silencer 20K in the present embodiment is configured such that a housing 38 consists of a mainframe 39A and an elastic material 40.

The mainframe 39, being configured so as to be exposed in a duct 2, has formed at its top plate 23 pores 22 in the present embodiment. This elastic material 40, being formed with a rubber material, for example, is configured so as to be elastically deformed by air pressure within the duct 2.

The silencer 20K having the configuration as described above is in a state such that, when the air speed of cooling air flowing in the duct 2 is low, the elastic material 40 is extended as illustrated in FIG. 19. On the other hand, with higher air speed of cooling air resulting in higher air pressure, the elastic material 40 is elastically deformed to decrease the volume of an air layer 24.

FIG. 20 illustrates a state such that the elastic material 40 is elastically deformed with an increase in air pressure. As illustrated, with higher speed of the cooling air generated at the fan 1, the elastic material 40 is elastically deformed to reduce the air layer 24 so that the thickness of the housing 38 is decreased. As a result, the distance L2 to the elastic material 40 from the pores 22 becomes shorter compared to the distance L1 to the elastic material 40 from the pores 22 prior to being elastically deformed as illustrated in FIG. 19 (L2<L<L1), enabling increasing the silencing frequency f of the silencer 20K based on equation (1) as described above.

Now, the peak frequency of the noise generated at the fan 1 depends on such factors as the number of rotations of the fan 1 and the number of blades provided at the fan 1. Then, assuming the peak frequency of the noise generated at the fan 1 as fp, the number of rotations of the fan 1 as Q, and the number of blades as M, it may be represented that: fp=Q×M×n (where n is an integer). Or as the number of rotations M of the fan 1 and/or the number of blades provided at the fan 1 change, or in other words as the speed of cooling air generated at the fan 1 changes, the peak frequency fp of the noise changes as well (the higher the fan speed, the higher the peak frequency fp).

However, the silencer 20K in the present embodiment is such that, even when the peak frequency fp of the noise generated at the fan 1 changes, a change in the speed of the cooling air resulting from the change in the peak frequency as described above is followed by a change in the silencing frequency f of the silencer 20K. Thus, the silencer 20K enables automatically optimizing the silencing effect, enabling effectively silencing the noise generated at the fan 1.

Next an eleventh embodiment of the present invention is described.

FIGS. 21 and 22 illustrate a silencer 20L being the eleventh embodiment. In the tenth embodiment as described previously, the configuration is such that the housing 38 is deformed using the elastic material 40, thereby enabling varying the thickness of the housing 38 (the length L of the noise passage). On the other hand, the silencer 20L in the present embodiment is characterized by having provided a shape memory alloy 42 (illustrated with bold lines) at a housing 41.

The shape memory alloy 42, having a bellows shape at room temperature as illustrated in FIG. 21, is set up between a top plate 23 having formed a pore 22 and a mainframe 39B shaped to have a bottom. This shape memory alloy 42 has a characteristic such that the bellow portion shrinks by being heated as illustrated in FIG. 22.

The silencer 20L being configured as described above is in a state such that the shape memory alloy 42 is extended in a bellows shape as illustrated in FIG. 21 when the duct 2 is at room temperature, or in other words when the material to be cooled by the fan 1 is adequately cooled. On the other hand, as the temperature of the duct 2 increases, the shape memory alloy 42 is heated so that the shape memory alloy 42 shrinks as illustrated in FIG. 22 and the volume of the air layer 24 within the housing 41 decreases.

The fact that the temperature of the duct 2 increases indicates that the cooling of the material to be cooled by the fan 1 is not performed adequately. Then, a control apparatus (not illustrated) for performing driving control of the fan 1 performs a control such that it detects when the temperature of the material to be cooled becomes higher than a predetermined value so as to increase the number of rotations of the fan 1 and to increase the speed of cooling air. This control enables preventing the temperature of the material to be cooled from becoming high.

As described previously, the peak frequency of the noise generated at the fan 1 depends on the number of rotations of the fan 1. Thus, when the temperature of the material to be cooled rises so as to increase the number of rotations of the fan 1, the peak frequency of the noise generated at the fan 1 increases.

However, the silencer 20L in the present embodiment is such that when the temperature of the material to be cooled rises so as to result in a rise in the temperature of the duct 2, a shrinking deformation occurs in the shape memory alloy 42 as illustrated in FIG. 22. Hereby, the distance L2 to the elastic material 40 from the pore 22 becomes shorter than the distance L1 to the elastic material 40 from the pore 22 prior to deformation as illustrated in FIG. 21 (L2>L1), thereby enabling increasing the silencing frequency f based on equation (1). Thus, even with the silencer 20L in the present embodiment, automatic optimizing of the silencing effect is enabled, enabling effective silencing of the noise generated at the fan 1.

Now a twelfth embodiment of the present invention is described.

FIGS. 23 through 26 illustrate a silencer 20M as the twelfth embodiment. FIG. 23 is a vertical cross-sectional view of the silencer 20M, FIG. 24 is a plan view of the silencer 20M, FIG. 25 is a plan view illustrating the state after operating the silencer 20M, and furthermore FIG. 26 is a cross-sectional view from the right-hand side of the silencer 20M.

The silencer 20M in the present embodiment is configured such that area-varying means varies the opening area of pores 43 being formed at top plate 59. This area-varying means is configured from such elements as a sliding plate 44, a permanent magnet 46, an electromagnet 47, a coil spring 48, and a top plate 59.

The top plate 59, as illustrated in FIGS. 24 and 25, has formed water-droplet shaped multiple pores 43. This top plate 59 is fixed to a housing 21 and all of the multiple pores 43 are configured so as to communicatively connect to an air layer 24 being formed within the housing 21. Moreover, the electromagnet 47 is set up at a predetermined position of the top plate 59.

The sliding plate 44 is mounted onto the center of the top of this top plate 59 so as to be movable in the direction as illustrated with an arrow between Y1 and Y2. More specifically, a pair of guides 49 for guiding the sliding plate 44 are set up at the top plate 59 so that the sliding plate 44 is guided by this pair of guides 49 so as to move in the direction as illustrated with the arrow between Y1 and Y2.

This sliding plate 44 has formed multiple long pores 45 extending in the direction (the direction as illustrated with the arrow between X1 and X2) orthogonal to the direction of the arrow between Y1 and Y2. The length W1 (below referred to as the width dimension W1) relative to the direction of the arrow between Y1 and Y2 of these long pores 45 is set to be smaller than the length W2 (below referred to as the width dimension W2) relative to the direction of the arrow between Y1 and Y2 of the pores 43 (W2>W1).

Moreover, the permanent magnet 46 is provided at one edge (the edge in the Y1 direction) of the sliding plate 44 such that the position of the permanent magnet is set facing the electromagnet 47 being provided at the top plate 59. Moreover, a coil spring 48 is set up between the edge of the sliding plate 44, that is set up with the permanent magnet 46, and the top plate 59.

As this coil spring 48 is elastically energized in the direction of shrinking, when there is no magnetic force generated at the electromagnet 47 as illustrated in FIG. 24, due to the elasticity of the coil spring 48, the sliding plate 44 is moved in the direction towards Y2 of the arrow illustrated (below referred to this state as the state prior to operating). Moreover, in the state prior to operating as illustrated in FIG. 24, the long pores 45 are overlapping with predetermined ranges at the side of the pores 43 that is in the direction towards Y2. Then, these overlapping portions configure the pores 22 for introducing the noise into the housing 21 (these pores 22 are illustrated as hatched).

In the configuration as described above, once current is supplied to the electromagnet 47, magnetic force is generated at the electromagnet 47. As the permanent magnet 46 is set up to face the electromagnet 47, with the permanent magnet 46 generating magnetic force, the sliding plate 44 moves in the direction toward Y1 of the arrow illustrated in opposition to the force of the coil spring 48. Then, the amount of movement of the sliding plate 44 in the direction towards Y1 may be controlled with the value of current supplied to the electromagnet 47 (or the magnetic force generated at the electromagnet 47), assuming the elastic energizing of the coil spring 48 to be constant.

Moreover, as described above, the pores 43 are made to be water-droplet shaped (or a shape such that the length of the pores 43 relative to the direction of the arrow between X1 and X2 as illustrated changes gradually when proceeding in the direction of the arrow between Y1 and Y2) and that the width dimension W1 of the long pores 45 is shorter than the width dimension W2 of the pores 43. Thus, the sliding plate 44 moving in the direction of the arrow between Y1 and Y2 changes the area of the portions overlapping between the pores 43 and the long pores 45, or the area of the pores 22.

According to equations (1) and (2) as described above, the larger the diameter φ of the pores, the larger the silencing frequency f. Moreover, as in the present embodiment, changing the area of the pores 22 where the pores 43 and the long pores 45 overlap is equivalent to changing the diameter φ of the pores in equations (1) and (2).

Thus, according to the silencer 20M in the present embodiment, moving the sliding plate 44 enables adjusting the value of the silencing frequency f, enabling wide-bandwidth silencing. Moreover, randomly varying the diameter of the opening of the pores enables, even when the frequency of noise changes, reliably responding to the change so as to perform silencing.

It is noted that the shape of these pores 43 is not limited to the water-droplet shape so that other shapes are possible as long as the area of the opening formed as a result of the overlapping of the pores 43 and the long pores 45 is shaped such that it changes as the sliding plate 44 moves. Moreover, it may be configured such that the area of the opening pores 22 increases as the sliding plate 44 moves with an increased speed of cooling air and as the sliding plate 44 moves with an increased supply voltage of the fan.

Next a thirteenth embodiment of the present invention is described.

FIGS. 27 through 29 illustrate a silencer 20N being the thirteenth embodiment. FIG. 27 is a perspective view of the silencer 20N, while FIGS. 28 and 29 are vertical cross-sectional views for describing the operation of the silencer 20N.

The silencer 20N in the present embodiment is also configured to provide area-varying means for varying the opening area of pores 22 being formed at a top plate 59. In the present embodiment, this area-varying means is configured only from elastic strips 50. Thus, compared to the silencer 20M in the twelfth embodiment described previously, simplified structure and low cost are achieved.

The elastic strips 50, being formed with an elastic material such as rubber, for example, are configured to integrally form a fixed section 50A and a movable section 50B. These elastic strips 50 are configured such that the movable section 50B makes a roughly-straight line with the fixed section 50A when there is no cooling air flowing within a duct 2 as illustrated in FIG. 28. Moreover, the elastic strips 50 are fixed at the positions close to the pores 22. More specifically, the elastic strips 50 are fixed to the bottom of a top plate 23 as the fixed sections 50A are adhered to the edges of the pores 22 that are on the side upstream relative to the direction “a” of flow of cooling air.

The silencer 20N being configured as described above is such that the elastic strips 50 as illustrated in FIG. 28 have the movable sections 50B making a roughly-straight line with the fixed sections 50A when the air speed of the cooling air flowing in the duct 2 is low (the speed of the noise flowing in the duct 2 is low). It is noted that the opening area of the pores 22 then is set as S1.

FIG. 29 illustrates the state in which the air speed of the cooling air flowing in the duct 2 is high (the speed of noise flowing in the duct 2 is high). As the air speed of the cooling air increases, the wind force acts on the movable sections 50B so as to cause the movable sections 50B to deflect toward the bottom side of a housing 24, resulting in a larger opening area of the pores 22. Then, when a predetermined air speed is reached, the moveable sections 50B are caused to be extended in a direction that is obliquely downward relative to the fixed sections 50A such that the opening areas of the pores 22 become the maximum area S2 (See FIG. 29).

According to equations (1) and (2) as described above, the larger the diameter φ of the pores, the larger the silencing frequency f. Moreover, as in the present embodiment, the fact that the area of the pores 22 changes is equivalent to changing the diameter φ of the pores according to the equations (1), (2).

Thus, according to the silencer 20N of the present embodiment, as the value of the silencing frequency f changes depending on the air speed of cooling air flowing in the duct 2, or the peak frequency of noise generated at the fan 1, performing a silencing process that follows a wide range of frequencies is enabled. Moreover, the silencing performance of the silencer 20N, being enabled to be changed by adjusting the elasticity coefficient of the elastic strip and the area of the pores 22 covered by the movable sections 50B, may be set to be a performance suitable for silencing noise generated at the fan 1. Thus, according to the silencer 20N, efficient silencing of the noise generated at the fan 1 is enabled.

Next a fourteenth embodiment of the present invention is described.

FIG. 30 illustrates a silencer 20P being the fourteenth embodiment. The silencer 20P in the present embodiment is characterized by having to configure a housing 51 with a heat sink 52 and a duct 53 (illustrated with a long-dashed short-dashed line).

The heat sink 52, for cooling such apparatuses as a semiconductor apparatus being provided in electronic equipment into which the silencer 20P is fit, is configured such that multiple fins 55, 56 are erected at the top of a base 61. The heat sink 52 in the present embodiment is configured such that a fin-without-pores 55 that has not formed pores 57 and a fin-with-pores 56 that has formed pores 57 are alternately juxtaposed.

Moreover, the duct 53, formed of a plate material in a horseshoe shape, is mounted onto the base 61 so as to cover each of the fins 55 and 56. Thus, with the duct 53 being mounted onto the heat sink 52, an air layer 24 being partitionally formed by an adjacent pair of the fins 55 and 56 is formed within the silencer 20P (See FIG. 33). Hereby, when the sound wave to be noise is introduced into the silencer 20P, this noise is silenced within the air layer 24 formed between an adjacent pair of the fins 55 and 56.

FIGS. 31 and 32 illustrate one example of a connecting structure for connecting the silencer 20P to a fan 1. In the example illustrated in FIG. 31, the silencer 20P is directly connected to the fan 1 so as to make a straight line with the fan. This connecting structure enables achieving reducing the total thickness of the fan 1 and the silencer 20P. Moreover, in an example illustrated in FIG. 32, a gap is provided between the position at which the fan 1 is set up and the position at which the silencer 20P is set up.

In either of the connecting structures, the cooling air generated at the fan 1 is introduced into a housing 51 from an inlet section 60 of the silencer 20P so as to be discharged into a duct 2 from a discharging section 62. Then, the cooling air passing within adjacent pairs of the fins 55, 56 causes dissipation of heat that is transferred to the heat sink 52 from a material to be cooled. On the other hand, the noise generated at the fan 1, being introduced into the silencer 20P from the inlet 60 with the cooling air, is silenced within the air layer 24 being formed between adjacent pairs of the fins 55, 56.

Thus in the silencer 20P in the present embodiment, as the housing 51 is configured with the duct 53 and the heat sink 52 that configure a cooling apparatus, the silencer 20P may be used for the cooling apparatus. Thus, achieving reducing the space of the electronic equipment in which the silencer 20P is provided, relative to the configuration such that a silencer and a cooling apparatus are provided separately, is enabled.

FIGS. 34 through 36 illustrate variants of the silencer 20P illustrated in FIGS. 30 through 33. As illustrated in FIG. 33, the silencer 20P as described previously is configured such that a fin-without pores 55 and a fin-with-pores 56 are alternately set up.

On the other hand, a silencer 20Q in a first variant as illustrated in FIG. 34 is configured such that all fins set up within a duct 53 are set to be the fins-with-pores 56 and that pores 57 are not communicatively connected (see the dashed line) between neighboring fins-with-pores 56. A silencer 20R in a second variant as illustrated in FIG. 35 is configured such that all fins set up within a duct 53 are set to be fin-with-pores 56 and that pores 57 are communicatively connected (see the dashed line) between neighboring fins-with-pores 56.

Moreover, a silencer 20S in a third variant as illustrated in FIG. 36 is characterized by having set up fins-without-pores 55 and fins-with-pores 56 alternately and having set up fins with pores 56 in a duct 53. Thus, randomly setting the way of setting up each of the fins 55, 56 and the position at which the pores 57 are formed are enabled, thereby enabling varying the silencing performance.

Next a fifteenth embodiment of the present invention is described.

FIG. 37 illustrates a silencer 20T being the fifteenth embodiment. The silencer 20T in the present embodiment is configured such that fins-without-pores 55 and fins-with-pores 56 are alternately juxtaposed as in the silencer 20P in the fourteenth embodiment as illustrated in FIG. 30. Furthermore, the silencer 20T in the present embodiment 20T is characterized by having provided a shielding plate 58 at each end of a mutually-facing pair of fins-without-pores 55 and fins-with-pores 56.

This shielding plate 58 is airproof fixed to a heat sink 52 and is configured so as to cause the space between the duct 53 and the shielding plate 58 to be airproof when the duct 53 is mounted onto the heat sink 52. Thus, the space (air layer 24) formed between the fins-without-pores 55, the fins-with-pores 56, a base 61, and the duct 53 is configured such that only pores 57 are communicatively connected to the outside while the other portions are airproof.

As described previously using FIGS. 5A and 5B, increasing the airproofness of the air layer 24 improves the silencing performance. Thus, as in the silencer 20T in the present embodiment, having provided the shielding plate 58 at both ends of mutually-facing pairs of the fins 55, 56 so as to increase the airproofness of the air layer 24 formed therein enables improving the silencing performance of the silencer 20T. 

1. A silencer, comprising: a housing having a flat enclosing shape and having formed therein a passage for silencing; and one or more pores, being formed at said housing so as to be communicatively connected with said passage, into which a sound wave to be noise is introduced; wherein said pores, being formed close to the periphery of said housing, are configured so that said sound wave to be noise travels in a planar direction of said housing.
 2. The silencer as claimed in claim 1, wherein one or more partition plates for partitioning said housing in the thickness direction are provided so as to form within said housing plural of the passages in which said sound wave to be noise travels.
 3. The silencer as claimed in claim 1, wherein a reflecting plate for reflecting toward said passage said sound wave to be noise is provided at said housing.
 4. The silencer as claimed in claim 1, wherein said housing is made airproof except for positions at which said pores are formed.
 5. A silencer, comprising: a housing having a flat enclosing shape and having formed therein an air layer for silencing; and a plurality of pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; wherein said pores are configured so as to make height positions from a surface of said housing from which said pores open to differ.
 6. The silencer as claimed in claim 5, wherein one or more pipes are provided at said pores so that by varying the lengths of said pipes, the height positions relative to the surface of said housing from which said pores open are varied.
 7. The silencer as claimed in claim 5, wherein varying the wall thickness of said housing varies depths of said pores being formed at said housing.
 8. A silencer, comprising: a housing having a flat enclosing shape and having formed therein an air layer for silencing; and a plurality of pores, being formed at said housing so as to be communicatively connected with said air layer, into which sound wave to be noise is introduced; wherein said pores are configured so as to make opening areas of said pores to differ.
 9. A silencer, comprising: a housing having a flat enclosing shape and having formed therein an air layer for silencing; one or more pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and area-varying means for varying opening areas of said pores.
 10. The silencer as claimed in claim 9, wherein said area-varying means is configured to vary, in order to make decreased opening areas, the opening areas of said pores when the speed of cooling air increases.
 11. A silencer, comprising: a housing having a flat enclosing shape and having formed therein an air layer for silencing; one or more pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and shape-varying means for varying thickness of said housing.
 12. The silencer as claimed in claim 11, wherein said shape-varying means is configured to decrease the thickness of said housing when the speed of cooling air increases.
 13. A silencer, comprising: a housing having an enclosing shape and having formed therein an air layer for silencing; and one or more inlet sections, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; wherein multiple fins for cooling having formed thereon one or more pores are provided within said housing.
 14. A silencer, comprising: a housing having an enclosing shape and having formed therein an air layer for silencing; and one or more inlet sections, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; wherein fins for cooling having formed one or more pores and fins for cooling not having formed one or more of the pores are juxtaposed; and a shielding plate is provided at each end of a pair of said fin for cooling with pores and said fin for cooling without pores.
 15. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having a flat enclosing shape and having formed therein a passage for silencing; and one or more pores, being formed at said housing so as to be communicatively connected with said passage, into which a sound wave to be noise is introduced; and wherein said pores, being formed close to the periphery of said housing, are configured so that said sound wave to be noise travels in a planar direction of said housing.
 16. The electronic equipment as claimed in claim 15, wherein one or more partition plates for partitioning said housing in a thickness direction are provided so as to form within said housing plural of the passages in which said sound wave to be noise travels.
 17. The electronic equipment as claimed in claim 15, wherein a reflecting plate for reflecting toward said passage said sound wave to be noise is provided at said housing.
 18. The electronic equipment as claimed in claim 15, wherein said housing is made airproof except for positions at which said pores are formed.
 19. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having a flat enclosing shape and having formed therein an air layer for silencing; and a plurality of pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and wherein said pores are configured so as to make height positions from a surface of said housing from which said pores open to differ.
 20. The electronic equipment as claimed in claim 19, wherein one or more pipes are provided at said pores so that by varying the lengths of said pipes, the height positions relative to the surface of said housing from which said pores open are varied.
 21. The electronic equipment as claimed in claim 19, wherein varying the wall thickness of said housing varies depths of said pores being formed at said housing.
 22. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having a flat enclosing shape and having formed therein an air layer for silencing; and a plurality of pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and wherein said pores are configured so as to make opening areas of said pores to differ.
 23. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having a flat enclosing shape and having formed therein an air layer for silencing; one or more pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and area-varying means for varying opening areas of said pores.
 24. The electronic equipment as claimed in claim 23, wherein said area-varying means is configured to vary, in order to decrease said opening areas, the opening areas of said pores when the speed of cooling air increases.
 25. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having a flat enclosing shape and having formed therein an air layer for silencing; and one or more pores, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and shape-varying means for varying thickness of said housing.
 26. The electronic equipment as claimed in claim 25, wherein said shape-varying means is configured to decrease the thickness of said housing when the speed of cooling air increases.
 27. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated at said fan, wherein the silencer comprises: a housing having an enclosing shape and having formed therein an air layer for silencing; and one or more inlet sections, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; and wherein multiple fins for cooling having formed one or more pores are provided within said housing.
 28. Electronic equipment, including within an apparatus mainframe a fan for cooling and a silencer for silencing noise generated by said fan, the silencer comprising: a housing having an enclosing shape and having formed therein an air layer for silencing; and one or more inlet sections, being formed at said housing so as to be communicatively connected with said air layer, into which a sound wave to be noise is introduced; wherein fins for cooling having formed one or more pores and fins for cooling not having formed one or more of the pores are juxtaposed; and a shielding plate is provided at each end of a pair of said fins for cooling with pores and said fins for cooling without pores. 